This invention relates to ink fountains and more particularly to a device for preventing the clogging of the ink metering gap of ink fountains by lint or other debris emanating from paper being printed.
The present invention relates to the problems caused by the accumulation of paper lint in the ink fountains of offset lithographic presses when used to print newspapers and the like. The paper used in offset lithographic newspaper printing operations is uncoated in comparison with clay coated stock fibers used in commercial printing. With uncoated stock, the paper fibers are exposed and, therefore, it is possible for the paper fibers to be torn from the paper during the printing process. These paper fibers are commonly referred to as lint. The fibers which are torn and removed from the web become mixed in with the ink and, for reasons not fully understood, are transported along the ink train and eventually collect either in the ink fountain or on the rider rollers.
As is typical in the type of offset lithographic presses involved, there is an ink fountain blade which with associated structure forms an ink fountain. The ink fountain blade and the ink fountain roller have an adjustable gap therebetween which controls the amount of ink on the ink fountain roller. It is this gap which can become narrowed by the accumulation of lint on the ink fountain roller.
Operatively associated with the ink fountain is, typically, an ink agitator which may be cone shaped which agitates or mixes the ink in the desired manner. The ink agitator is connected to a structure such as that shown and described in a number of U.S. Pat. such as Nos. 3,848,529, 2,849,952, and 3,084,025 so that the cone shaped ink agitator rotates in an antirolling direction and traverses back and forth through the ink fountain so as to agitate and mix the ink.
It has been found that the lint which collects in the ink fountain is carried there by the ink train. In other words, the ink fountain roller is contaminated by lint because the lint is carried to the ink fountain by the roller train. This lint is then carried into the ink fountain by the film of ink on the fountain roller. While not completely understood, it is believed that as the film of ink exits from the ink fountain it is subjected to a shearing force which causes the lint to remain on the ink roller. The lint builds up on the ink fountain roller and is believed to be the primary cause for narrowing the metering gap. Eventually the lint on the fountain roller is dislodged causing further clogging of the metering gap.
The problem is that when lint collects or builds up on the ink fountain roller it can cause clogging of the ink metering gap formed at the juncture or nip of the ink fountain blade and the ink fountain roller. Since this metering gap governs the amount and/or thickness of ink which is fed onto the fountain roller, and to the ink roller train to the printing plate, clogging of the gap causes a starvation or reduction in the amount of ink feed to the train. When this occurs, the normal reaction of the pressman is to assume that more ink is needed and thus he makes an adjustment in order to increase the size of the gap between the ink fountain blade and the ink fountain roller. Frequently, when the gap is increased the buildup of debris in the gap is swept away, leaving a gap that is too wide, rsulting in too high an ink flow. The pressman must then close down the gap. Aside from occupying the pressman with a wasteful task, this problem also results in spoilage and paper waste in addition to the ink loss.
Pressmen experienced in the art are familiar with the problem of lint clogging the ink fountain nip. Consequently, when a reduction in ink feed occurs, the experienced perssman knows that widening the fountain metering gap is not the proper corrective action because, as described above, this will subsequently lead to too high a feed rate. Thus, the experienced pressman will attempt to correct the problem by sticking an ink knife or other sharp pointed device into the gap between the fountain blade and fountain roller to loosen the lint which is clogging the gap. While this generally succeeds in correcting the problem by loosening the lint, this remedy is only temporary since the lint will again collect and again clog the nip.
Another attempt to solve this problem is to provide the ink fountain roller with a spiral groove. However, this proposal is negated if the groove is not kept clean so as to avoid filling in with a mixture of lint and ink.
Another proposed solution which has been tried, is to use an ink agitator equipped with a cone having a very sharp point. The purpose of this approach is to accomplish automatically what the pressman does with his ink knife; namely, remove the lint which is clogging the gap. Although this approach has been tried on many occasions over the years, it requires accurately positioning the sharp edge in the ink metering nip, over the entire length of the fountain. Since the fountain may be as long as 68 inches on large newspaper presses, it has been proven to be very difficult to obtain such accuracy.